Recently I have updated the JCE editor from 2.8.2 to 2.8.3.
When I try to upload content from the JCE file browser, it is throwing an error saying:
The server returned an invalid JSON response.
Seems the file is getting uploaded but the error is been thrown. Everything was working fine in the previous version 2.8.2.
I think these links will help you:
Invalid JSON response in JCE File Browser (Joomla - StackExchange)
The server returned an invalid JSON response. (JCE Forums)